1. Field of the Invention
The present invention relates to a method and apparatus for producing and displaying spatially-multiplexed composite images of three-dimensional imagery for use in stereoscopic viewing thereof substantially free of visual-channel cross-talk, stereoscopic asymmetric distortion, and color-intensity distortion.
2. Brief Description of the Prior Art
The use of stereoscopic imaging in modern times has gained increasing popularity. The reason for this trend in technological innovation is quite clear. At birth, each human being is endowed with the power of stereoscopic vision, and it is this power alone that enables human beings to view the world and all its inhabitants in three dimensions with full depth perception.
Presently, there exist a number of known techniques for recording and displaying stereoscopic images of three dimensional (3-D) objects and scenery, whether of real or synthetic nature. In the art of stereoscopic video imaging, in particular, two principally different techniques are presently being used to record and display stereoscopic images. The first technique is commonly referred to as "time-multiplexed" or field-sequential" stereo video, whereas the second technique is commonly referred to as "spatially multiplexed" stereo video.
In general, each of these stereo-imaging techniques involve image recording (i.e. generation) and image display processes. During the image generation process, left and right perspective images (or sequences of perspective images) of 3-D scenery are produced and subsequently recorded on a suitable recording medium. Preferably, the recorded left and right perspective images are produced (e.g. recorded, synthesized or otherwise captured) as if actually viewed with the inter-pupil distance of a human observer, or a stereoscopic camera with a desired viewing perspective. Then, during the image display process, the visible light associated with the left and right perspective images is visually presented to the left and right eyes of viewers, respectively, while minimizing the amount of visible light from the left and right perspective images that impinge upon the right and left eyes of the viewer, respectively. Failure to satisfy this condition during the display process results in the production of "visual-channel cross-talk," a phenomena which degrades 3-D depth perception and causes unbearable eye and brain fatigue during viewing. Inasmuch as the left and right perspective images of the 3-D scenery are viewed substantially by the left and right eyes of the viewer, respectively, a stereoscopic image of the 3-D scenery is perceived, complete with full spatial and depth information of the actual 3-D scenery, whether of real or synthetic nature.
The differences between the two above-described techniques reside primarily in the manner in which left and right perspective images are "channeled" to the left and right eyes of the viewer in order to preserve stereoscopy. These techniques will be briefly described below.
In 3-D video display systems based upon "time-multiplexing" principles, the left and right perspective images of 3-D scenery are displayed to viewers during different display periods (i.e. left and right perspective image display periods). To ensure that only left perspective images of the 3-D scenery are presented to the left eyes of viewers, the right eye of each viewer is not allowed to view the pixels of the left perspective image during the left perspective image display period.
Similarly, to ensure that only right perspective images of the 3-D scenery are presented to the right eyes of viewers, the left eye of each viewer is not allowed to view the pixels of the right perspective image during the right perspective image display period. In the contemporary period, this perspective image "blocking" or selective viewing process is achieved using a pair of liquid crystal light valves(LCLV) as the lenses in special eye wear (e.g. goggles ) worn by each viewer using a 3-D image viewing system based on such principles. Typically, a controller is required in order to drive the left LCLV lens during each left perspective image display period, and drive the right LCLV lens during each right perspective image display period.
In 3-D video display systems based upon "spatial-multiplexing" principles, left and right perspective images of 3-D scenery are spatially filtered using complementary filtering functions and thereafter the spatially-filtered perspectives images are combined during the image generation process to produce a composite spatially multiplexed image (SMI). Then during the image display process, the visible light associated with the left and right perspective image components of the composite image are simultaneously displayed, but with spatially different "polarizations" imparted thereto using a micropolarization panel of the type described in Applicant's U.S. Pat. No. 5,327,285, and copending application Ser. No. 08/126,077, both incorporated herein by reference in their entirety. To ensure that only left perspective images of the 3-D scenery are presented to the left eyes of viewers, the right eye of each viewer must not be allowed to view the pixels of left perspective images. Similarly, to ensure that only the right perspective images of the 3-D scenery are presented to the right eyes of viewers, the left eye of each viewer must not be allowed to view the pixels of right perspective images. Typically, this perspective image "blocking" or selective viewing process is achieved using a pair of inexpensive, spatially different polarizing lenses mounted in eye wear (e.g. spectacles) worn by each viewer using the 3-D video display system based on such principles of operation.
While each of these above-described 3-D image display techniques may be used to display 3-D color or gray-scale images, systems based on such techniques are not without shortcomings and drawbacks.
In particular, 3-D image display systems based upon "time-multiplexing" principles are notoriously plagued by "image flicker" problems. While 3-D video display systems based upon "spatial-multiplexing"principles are inherently free from the "image flicker" problem associated with time-multiplexed 3-D display systems, spatial-multiplexing 3-D display systems require the use of carefully constructed "micropolarization panels" mounted onto display surfaces (e.g. flat LCD panels, LCD projectors, etc.) from which the polarized light of spatially-multiplexed images emanates towards the eyes of the viewers.
While U.S. Pat. No. 5,327,285 and application Ser. No. 08/126,077 teach how to make and use SMI display systems capable of stereoscopic viewing of 3-D objects with image quality and resolution, Applicant hereof has discovered that when using phase-retarding micropolarization panels (i.e. micro-retardation arrays) as taught therein, a small yet significant amount of visual-channel cross-talk is inherently produced during the stereoscopic viewing process. The source of such visual channel cross-talk has been traced to the phase-retarding pattern(s) embodied within the micropolarization panel of such SMI display system. The phase retardation required to achieve either the P1 or P2 polarization state at each pixel location along the micropolarization panel is a strong function of wavelength of the illuminating backlight which, for example, in color LCD panels, varies significantly over each pixel location due to the RGB subpixel filters employed therein. Thus, when using phase-retarding micropolarization panels in prior art SMI display systems, it has been impossible to impart only a P2 polarization state to light rays emanating from left image pixels displayed along the LCD panel, and only a P1 polarization state to light rays emanating from right perspective image pixels displayed therealong. As a result, visual channel cross-talk introduced by the less than ideal phase characteristics of phase-retarding micropolarization panels results in the viewing (i.e. perception) of "double-images" slightly shifted in space, rather than spatially cohering as a unified stereoscopic image providing full 3-D depth sensation in the human vision system of the viewer.
In addition to visual-channel cross-talk, such SMI display systems also suffer from "asymmetric distortion" created during stereoscopic viewing of polarized SMIs produced from phase-retarding micropolarization panels mounted upon the display surface of SMI display structures. The cause of this asymmetric distortion is related to the fact that only one eye of a viewer of a displayed SMI perceives through passive polarizing eyeglasses ,a perspective image whose color has been distorted by virtue of the wavelength-dependent phase retardation which the spectral components of the perspective image undergo while passing through the micropolarization panel.
Moreover, the chromatic distortion of SMIs caused by the wavelength-dependent phase-retardation errors introduced by the imperfect retardation characteristics associated with such micropolarization panels degrades the color fidelity of 3-D imagery perceived by viewers using such stereoscopic display systems.
Collectively, the visual channel cross-talk, asymmetric distortion and chromatic distortion associated with prior art phase-retarding micropolarization display panels inherently degrades the degree of stereo separation achievable between the polarization-encoded visual channels of such stereoscopic display systems, and thus the overall stereoscopic viewing experience achievable therewith.
Thus, there is a great need in the art for an improved system and method for stereoscopic viewing 3-D objects represented in either grey-scaled or color spatially-multiplexed images, while avoiding the shortcomings and drawbacks of prior art apparatus and methodologies.